Wave shaping device using saturable inductance



March 29, 1966 w. J. BARTIK 3,243,734

WAVE SHAPING max/1cm USING SATURABLE mnucmncm Filed Oct. 51, 1963 UnitedStates Patent 3,243,734 WAVE SHAPING DEVICE USING SATURABLE INDUQITANCEWilliam .I. Bartik, Jenkintown, Pa., assignor to sperry RandCorporation, New York, N.Y., a corporation of Delaware Filed Oct. 31,1963, Ser. No. 320,463 6 Claims. (Cl. 333-40) This invention relates toa device which is utilized to shape electrical signals or waveforms.More particularly, the device uses transmission line techniques and thinmagnetic film phenomenon to provide a signal which has a leading edge orwave front which is steeper than an applied signal.

In the electronic field, there are many types of circuits which requirehigh speed signals to effect switching or operation thereof. In manycases, the operation of the circuit is accomplished entirely by thehigh-speed, fast rise-time leading edge of an applied signal. Many typesof circuits have been devised in order to provide such high-speed, fastrise-time signals. These circuits .include circuits for generating spikesignals and the like. However, these signal generating circuits aregenerally of a complicated and complex nature. Therefore, the instantdevice is proposed in order to provide a wave shaping device which isrelatively simple and uncomplicated.

In the instant invention, a two conductor transmission line, of eitherplanar or coaxial configuration, is provided. The spacer between theconductors of the transmission line includes an insulation layer and athin magnetic film layer. By using a thin magnetic film layer whichexhibits uniaxial anisotropy, variations may be made or effected in thepropagation of a signal supplied to the transmission line conductors. Byproperly controlling these variations, the leading edge or wave front ofthe applied signal may be varied such that the leading edge or wavefront of the signal produced is much steeper, i.e., has a faster risetime, than the originally applied signal.

It is an object of this invention to provide a device for easilygenerating signals having wave fronts with fast rise-times.

Another object of this invention is to provide a device which iscomprised of passive means and generates a Waveform with a steep-slopeleading edge.

Another object of this invention is to provide a signal forming networkwhich utilizes a transmission line having a thin magnetic layer includedin the spacer between the conductors of the transmission line.

These and other objects and advantages of this inven- .tion will becomemore readily apparent when the following description is read inconjunction'with the attached drawings, in which:

FIGURE 1 is a schematic diagram of one embodiment of the invention;

FIGURE 2 is a graphic diagram showing the hysteresis characteristic forthe thin magnetic film and the applied signals;

FIGURE 3 is a graphic representationof the originally applied signal andthe signal which is developed by the instant invention; and

FIGURE 4 is a schematic diagram of another embodiment of the instantinvention.

Referring now to FIGURE 1, there is shown one embodiment of the instantinvention. This embodiment comprises a transmission line element 100which is characterized by a coaxial configuration. That is, element 100is in the form of an elongated cylinder having two conductors in whichone conductor completely surrounds the other, the two conductors beingcoaxial and separated by a dielectric spacer. The inner conductor 18 maybe any electrically conductive material, as for example, copper, silveror the like. The dimensions of the inner conductor are determined by thepower to be carried by the device, the frequency of the signals to beapplied and other parameters which are determined by the usage of thedevice. Typically, inner conductor 18 may have a diameter ofapproximately /8 inch. Outer conductor 10 is similar to inner conductor18 in that it is an electrical conductor comprised of material such ascopper, silver or the like. The thickness of outer conductor 10 may beon the order of 0.01 inch. Typically, the thickness of conductor 10 isdetermined by the skin depth of the signal applied to the device. Thelength of the device is determined as a function of the wavelength ofthe applied signal. The device must be at least M4 long in order thatthe leading edge of the signal can be affected.

The thin magnetic film layer 14 may be any type of thin magnetic film asfor example the usual Permalloy magnetic material which is comprised ofNi and 20% Fe. This magnetic layer may have a thickness of approximately10,000 A. and is the same length as the inner and outer conductors. Thethin magnetic film layer is further characterized by a uniaxialanisotropy whereby HARD and EASY magnetization directions are exhibitedby the film. That is, by applying a signal to the EASY or HARDdirection, a different hysteresis characteristic is observed. In orderto avoid the losses produced by the open or rectangular hysteresischaracteristic, a thin magnetic film layer is provided with the EASYdirection along the axis of the cylinder. In addition, the HARDmagnetization direction of the thin film is defined to be in acircumferential direction around the axis of the cylinder.

The insulation layers 12 and 16 may be any desirable type of insulationsuch as SiO which may be on the order of 300 A. in thickness. Moreover,one or the other of the insulation layers 12 or 16 may be omitted, ifdesired. That is, only one of the insulation layers is required in orderto prevent electrical contact between the inner and outer conductors.The construction of element shown in FIGURE 1, is a coaxial transmissionline element which comprises the conductors 10 and 18. The spacerbetween. the conductors comprises insulation layers 12 and/or 16'andthin magnetic film layer 14 as well as any desirable bonding layers (notshown). In accordance with well known transmission line theory, theapplication of an input signal to one end of the transmission linebetween the inner and outer conductors results in the propagation of asignal therealong. The velocity of the propagation of the signal isgiven by the equation The values of ,u and e are characteristics of thespacer of the device. Because of the nature of the spacer, it isrelatively simple to vary the value of ,u thereof and to hold the valueof e substantially constant. By varying the value of u, a variation inthe propagation velocity of the signal is produced. If the propagationvelocity of the signal is varied during the signal duration, then .thewaveform of the signal produced is also varied. Thus, a waveformingoperation is produced by the transmission line element.

Referring now to FIGURE 2, the graphic illustration of the hysteresischaracteristic of the thin magnetic layer and the applied input signalshows more details of the operation of the device shown in FIGURE 1. Thehysteresis characteristic 200 is the substantially linear hysteresischaracteristic which is observed when a signal is applied to themagnetic material in the HARD magnetization direction thereof. Thishysteresis characteristic represents a Substantially lossless operationand includes the saturation levels 202 and 204 and the unsaturatedregion 206. The hysteresis characteristic 200, as shown by the solidline, is the idealized characteristic for the magnetic material 14. Whenthe film is operating in the negative saturation region 202 or thepositive saturation region 204-, the value of i thereof is approximatelyidentical to the value of a for air. On the contrary, when the film isoperating in the unsaturated region 206, the value of p. thereof maybein excess of 10,000. These changes in the value of ,U. vary theinductance and coupling between the inner and outer conductors of thetransmission line whereby the velocity of propagation of signalstherealong also varies.

It is generally well understood in the art that the idealized hysteresischaracteristic 200 (solid line) is relatively unobtainable. Therefore,the idealized characteristic is shown only so that the anisotropy valuesmay be conveniently defined by the points 212 and 214. In practice, thehysteresis characteristic incorporates rounded corners 208 and 210. Thevalue of ,4 which is related to the slope of the hysteresischaracteristic, varies continuously (rather than discontinuously) fromthe saturated to the unsaturated region, and vice versa, with therounded characteristic. As will become apparent subsequently, thiscontinuous slope variation provides a smoother output signal.

The applied signal 250 is shown as a sinusoidal signal having typicalsine Wave leading and trailing edges. The portion of the signal which iscentered about the B axis (line 220) of the hysteresis characteristic200 and which lies between the dashed lines 216 and 218 is the portionof the signal which causes the thin magnetic film layer to operate inthe unsaturated region. This portion of the sinusoidal applied signal isdesignated as 252. The peaks 254 of the applied signal which exceed thedashed lines 216 and/or 218 are the portions of the applied signal whichcause the thin magnetic film layer to operate in the saturated region.That is, the dashed lines 216 and 218 are projected from the knees orcorners 212 and 214, respectively, of the hysteresis characteristic 200.The points 212 and 214 represent the negative and positive anisotropyvalues, respectively, of the magnetic material. Of course, in practice,there are no discrete knees 212 or 214 as such but rather the slopes 208and 210 exist instead.

Referring now to FIGURE 3, there is shown, in solid line, a sinusoidalinput signal similar to signal 250 of FIGURE 2. The signal 300 producedby the waveforming device is shown by the dashed lines. Furthermore, the+H and H values for the magnetic material in the waveforming device arerepresented by the dashed lines 218 and 216, respectively. The signalportion 252 is the portion of the signal which is characterized by aninstantaneous amplitude which is lower than the magnitude of theanisotropy value H so that the magnetic material operates in theunsaturated region. Therefore, the signal 250, as supplied to thewaveforming device, has the portion 252 thereof delayed. The delayedportion of the leading edge of the signal is represented by the dashedline 302. would be parallel to the solid line portion 252 of the inputsignal. However, due to the curvature of the more realistic hysteresischaracteristic, including corners 208 and 210, shown in FIGURE 2, thevalue of a for the magnetic layer and, therefore, the inductance of thewaveforming device varies whereby the dashed line portion 302 approachesand coincides with the solid line portion 252. In the preferredembodiment, this coincidence of the signals will occur at the saturationlevel of the magnetic film. If the coincidence does not occur preciselyat this level, a slight discontinuity in the output signal may occurbetween the dashed signal portion 302 and the solid signal portion 254.That is, since the signal portion 254 is that portion of the appliedsignal which has the instantaneous amplitude greater than the magnitudeof the saturation value H this portion of the signal sees a saturatedmagnetic layer such that there is no delay thereof. T herefore, thesolid line portion 254 of the input signal 250 is indicative of andcoincident with the output signal which is produced thereby. Similarly,when the applied signal begins the negative slope of the trailing edgethereof, the magnitude of signal 250 (represented by the solid line)falls below the saturation value H whereupon the dashed signal portion304 is shown delayed with respect to the solid line signal portion 252a.Ag-ain, when the signal 250 reaches the crossover point at referenceline 220, the negative portion of the signal which has an instantaneousamplitude less than H is delayed because of the 'characteristics of thewaveforming device. This delayed signal is represented by the dashedsignal 302. Again, the negative signal portion 254 which has aninstantaneous amplitude greater than the negative saturation level, H;;,is not delayed because the value of ,u. of the magnetic material forthis portion of'the signal is small. The signal portion 252a, which isthe portion of the applied signal which has instantaneous amplitude lessthan the negative saturation value -H provides the delayed signalportion represented by dashed line 304. This type of operation continuesas long as input signals are applied to the waveforming device.

Thus, it may be seen that a typical sinusoidal input signal may beapplied to the waveforming device. The portion of this signal for whichthe instantaneous ampli tude is less than the absolute magnitude of thesaturation level of the thin magnetic layer material in the waveformingdevice is delayed. On the other hand, the portion of the applied signalfor which the instantaneous amplitude is greater than the absolutemagnitude of the saturation level of the thin magnetic film material isundelayed. Therefore, there is a bunching or shaping of the leading edgeof the signal. That is, part of the signal is delayed such that anotherpart of the signal appears substantially closer thereto in time wherebya signal is produced which has a faster rise time on the leading edgesthereof. Of course, the delay of the signal while the film is in theunsaturated region also'etfects the trailing edge of the signal wherebya less rapid trailing edge is produced. However, as noted supra, thereare many types of circuits which require high speed triggering pulseswherein a pulse with a fast-rise-time leadingedge may operate as thetriggering pulse and the slowspeed trailing-edge would beinconsequential. Moreover, this slow-speed trailing-edge of the signalwould not produce any spurious results which would interfere with theoperation of the high-speed leading-edge of the following oppositepolarity pulse. Therefore, a signal with a high-speed fast-rise-timeleading-edge is produced.

Referring now to FIGURE 4, there is shown another embodiment of theinvention. That is, the coaxial struc ture shown in FIGURE 1 has beenaltered to form a Under idealized conditions, the dashed line 302 planarconfiguration. In the embodiment shown in FIG URE 4, similar componentshave the last two digits thereof similar to elements or components shownin FIGURE 1. Thus, the transmission line conductors which are fabricatedof electrically conductive material, as for example, copper or silver,are designated as conductors 410 and 418, respectively. The insulatinglayers 412 and 416 (one of which may be eliminated if so desired) may beSiO layers which provide electrical insulation between the conductors410 and 418. Again, the layer 414 is a magnetic material in the form ofa thin magnetic film comprising a typical Permalloy material, as forexample Ni, 20% Fe. The operation of this device when an input signal isapplied thereto is identical to the operation of the device shown inFIGURE 1. Thus, the application of an input signal of alternatingconfiguration, as for example a sinusoidal input signal, provides a delayed signal for the portion of the signal for which the instantaneousamplitude is less than the absolute magnitude of the saturation levelsof the thin magnetic film 414. The portions of the input signal forwhich the instantaneous amplitude is greater than the saturation levelsof the film 414 are undelayed. Therefore, the bunching of the leadingedge of the applied signal occurs whereby a signal is produced which hasa high-speed, fast rise-time leading edge.

The specific embodiments described spura are not meant to be limitativeof the instant invention. Rather, these specific embodiments are meantto provide preferred illustrations of the inventive principles describedherein. Therefore, modifications of the device may be made withoutdeparting from the principles and scope of the invention as described inthe attached claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A waveshaping element to receive electrical signals of asubstantially sinusoidal configuration and to produce electrical signalshaving a steeper leading edge than the signal received, said elementcomprising first and second parallel electrical conductors, a thinmagnetic film layer exhibiting uniaxial anisotropy and havingmagnetically saturated and unsaturated operating conditions, at leastone layer of insulating material, said magnetic layer and saidinsulating material being disposed between said first and secondelectrical conductors, said element producing a substantial delay onlyfor electrical signals received thereby for which the instantaneousamplitude is such that said thin film operates in the unsaturatedoperating condition, said element producing substantially no delay forsignals received thereby for which the instantaneous amplitude is suchthat said thin film operates in the saturated operating condition.

2. A waveshaping element to receive electrical signals of asubstantially alternating configuration, said element comprising firstand second parallel electrical conductors, said first and secondconductors being arranged in coaxial and concentric relationship, a thinmagnetic film layer exhibiting uniaxial anisotropy and havingmagnetically saturated and unsaturated operating conditions, a layer ofinsulating material, said magnetic layer and said insulating materialbeing disposed between said first and second electrical conductors incoaxial and concentric layers, said element producing a substantialdelay only for electrical signals received thereby for which theinstantaneous amplitude is small enough such that said thin filmoperates in the unsaturated operating condition, said element producingsubstantially no delay for signals received thereby for which theinstantaneous amplitude is large enough such that said thin filmoperates in the saturated operating condition.

3. In a waveshaping device, a pair of parallel electrical conductors, athin magnetic film exhibiting uniaxial anisotropy, an electricallyinsulating layer, said thin film and said insulating layer beingdisposed between said pair of parallel conductors, said thin film beingcharacterized by EASY and HARD magnetization directions, said thin filmbeing oriented relative to said pair of conductors such that electricalsignals which are applied to the conductors propagate therealongparallel to said thin film EASY magnetization direction wherebysubstantially lossless operation is achieved, said thin magnetic filmfurther characterized by saturated and unsaturated operating conditionswhich affect the propagation of electrical signals along said pair ofconductors.

4. In a waveshaping device, a pair of parallel coaxial electricalconductors, magnetic film layer exhibiting uniaxial anisotropy, anelectrically insulating layer, said magnetic film layer and saidinsulating layer being concentric layers and disposed between said pairof parallel conductors, said magnetic film layer being characterized byEASY and HARD magnetization directions, said magnetic film layer beingoriented relative to said pair of conductors such that electricalsignals applied to the conductors propagate therealong parallel to saidthin film EASY magnetization direction whereby substantially losslessoperation is achieved, said magnetic film layer further characterized bysaturated and unsaturated operating conditions which afiYect thepropagation of electrical signals along said pair of conductors, saidunsaturated operating condition being efiective to delay signals appliedto said pair of conductors, said saturated operating condition eifectingsubstantially no delay to signals applied to said pair of conductors.

5. In a waveshaping device, a pair of parallel electrical conductors, athin magnetic film exhibiting uniaxial anisotropy and characterized byEASY and HARD magnetization direction, an electrically insulating layer,said thin film and said insulating layer being disposed between saidpair of parallel conductors, said thin film being oriented relative tosaid pair of conductors such that electrical signals which are appliedto the conductors propagate therealong parallel to said thin film EASYmagnetization direction whereby substantially lossless operation isachieved, said thin magnetic film further characterized by saturated andunsaturated operating conditions which atfect the propagation ofelectrical signals along said pair of conductors to the extent that thesignal portion Which causes said thin film to operate in the unsaturatedcondition is delayed while the signal portion which causes said thinfilm to operate in the saturated condition is not delayed whereby thedelayed signal portion is produced closer to the undelayed signalportion.

6. A waveshaping element for receiving electrical signals of asubstantially sinusoidal configuration and producing electrical signalshaving a steeper leading edge than the signal received, said elementcomprising first and second parallel electrical conductors, a thinmagnetic film layer exhibiting uniaxial anisotropy and havingmagnetically saturated and unsaturated operating conditions, thesaturation level between said saturated and unsaturated operatingconditions being defined by the anisotropy field value of said thinmagnetic film layer, at least one layer of insulating material, saidmagnetic layer and said insulating material being disposed between saidfirst and second electrical conductors, said element producing asubstantial delay only for electrical signal portions received therebyfor which the instantaneous amplitude is greater than said saturationlevel of said thin film, said element producing substantially no delayfor electrical signal portions received thereby for which theinstantaneous amplitude is less than said saturation level of said thinfilm whereby the delayed signal portions are produced substantiallycloser to the undelayed signal portions,

References Cited by the Examiner UNITED STATES PATENTS 2,871,453 1/1959Bradley 333-31 3,051,891 8/1962 Jorgensen 323-76 3,102,048 8/1963 Granet al 340-174 3,175,200 3/1965 Hofiman et al. 340174 HERMAN KARLSAALBACH, Primary Examiner.

A. M. MORGANSTERN, Assistant Examiner.

1. A WAVESHAPING ELEMENT TO RECEIVE ELECTRICAL SIGNALS OF ASUBSTANTIALLY SINUSOIDAL CONFIGURATION AND TO PRODUCE ELECTRICAL SIGNALSHAVING A STEEPER LEADING EDGE THAN THE SIGNAL RECEIVED, SAID ELEMENTCOMPRISING FIRST AND SECOND PARALLEL ELECTRICAL CONDUCTORS, A THINMAGNETIC FILM LAYER EXHIBITING UNIAXIAL ANISOTROPY AND HAVINGMAGNETICALLY SATURATED AND UNSATURATED OPERATING CONDITIONS, AT LEASTONE LAYER OF INSULATING MATERIAL, SAID MAGNETIC LAYER AND SAIDINSULATING MATERIAL BEING DISPOSED BETWEEN SAID FIRST AND SECONDELECTRICAL CONDUCTORS, SAID ELEMENT PRODUCING A SUBSTANTIAL DELAY ONLYFOR ELECTRICAL SIGNALS RECEIVED THEREBY FOR WHICH THE INSTANTANEOUSAMPLITUDE IS SUCH THAT SAID THIN FILM OPERATES IN THE UNSATURATEDOPERATING CONDITION, SAID ELEMENT PRODUCING SUBSTANTIALLY NO DELAY FORSIGNALS RECEIVED THEREBY FOR WHICH THE INSTANTANEOUS AMPLITUDE IS SUCHTHAT SAID THIN FILM OPERATES IN THE SATURATED OPERATING CONDITION.